As far as I understand the story, Advent enclave had a lot of water - it was literally founded on a spring or something - but then Initiative asked Ryder to use seismic hammers to employ seismic activity that Architect was causing to redirect water to Prodromos. In the result Advent started to lose water, and they went to investigate. The last seismic hammer can be used either to steal the rest of their water for the Initiative; or to open gas deposit, that Advent is willing to mine for the Initiative. Advent would still like to be paid for their work with *mining*, but they would be providing resulting gas to Initiative, which clearly implies that it would be of great use to Prodromos. An alternative is to make it a bit easier for Prodromos to have some irrigation with the stolen water, at the cost of hundreds of dead Advent citizens - and no gas for Initiative.
So no, it was not architect itself, it was not that Advent was stupid - Initiative is asking Ryder to steal water from their neighbors, and to sentence them to death in the result RATHER THAN to have some good neighbors that are willing to work for Initiative as gas miners.
Two additional points:
- Advent made it very clear that they are not against the Initiative, but that they simply do not trust Tann, and just decided to go independent. They are happy to see Pathfinder, to cooperate with Prodromos, and generally to share land, and to "invite others to their capitol".
- Prodromos has enough water to sustain all their needs; they wish for water so they can grow more plants. And taking into account that Initiative has access to huge resources of water on Veold, it is not even realistic "need" - it is just a convenience.
So no, I do not believe that Advent is stupid, or that they deserve to die because of Initiative's greed. I believe that they can occur to be good neighbors, and that it is worthwhile to cooperate with them as much as Initiative can. Anything else means that Ryder turns into something like Sloane or those dead Angarans from Kurinth's Valley on Kadara.